Gated computed tomography

ABSTRACT

A computed tomography system ( 100 ) includes a windowing component ( 140 ) that receives an ECG signal that includes a premature heart cycle. The ECG signal is time-synchronized with x-ray projection data of a beating heart. The windowing component ( 140 ) either removes or repositions a first reconstruction window within a first heart cycle to correspond to a desired cardiac phase when the premature heart cycle causes the first reconstruction window to correspond to a different cardiac phase, based on available data. A reconstructor ( 148 ) that reconstructs projection data corresponding to a plurality of reconstruction windows from different cardiac cycles generates image data indicative of the desired phase of the heart.

The present application generally relates to imaging systems. Inparticular, it relates to computed tomography (CT) and, moreparticularly, to generating and detecting radiation and processing dataindicative thereof.

Computed tomography (CT) imaging often includes scanning an object inmotion. For example, cardiac CT imaging includes scanning a beatingheart. With cardiac CT, it typically is more desirable to reconstructdata corresponding to a phase of the heart cycle in which the heart isrelatively motionless. Various techniques including electrocardiogram(ECG) signal gating have been used to locate projection datacorresponding to such a phase within projection data representative ofthe heart cycle(s).

With retrospective gating, electrical activity of the heart, whichreflects the state of the heart throughout a heart cycle, is sensed byan electrocardiograph while a beating heart is scanned. Datacorresponding to a desired heart phase is then gated (selected) andreconstructed based on the signal representing the electrical activity.The data is selected to obtain projection data collected over an angularrange that provides a complete CT data set.

In one instance, the cardiac scanning procedure detects projection dataover multiple successive heart cycles. A sub-set of data for each heartcycle corresponding to the desired phase is then selected forreconstruction. Reconstructing data from multiple heart cycles canimprove temporal resolution. However, an irregular heart rhythm, whichgenerally is unpredictable, can change one or more heart cycles relativeto the average heart cycle. This may result in the selection of datacorresponding to a different cardiac phase. As a consequence, thereconstructed image data may be degraded.

One attempt to improve the quality of such data is discussed inCademartiri F. et al., Improving diagnostic accuracy of MDCT coronaryangiography in patients with mild heart rhythm irregularities using ECGediting, AJR Am J Roentgenol. 2006 March;186(3):634-8. Cademartiri F. etal. describes a manual technique in which a user deletes a window thatidentifies data for reconstruction for a heart cycle if the heart cycleis followed by a premature heart cycle and, if this results ininsufficient data for reconstruction, adds such a window(s) to thepremature heart cycle. Unfortunately, the quality of resulting imagedata may be less than desired based on the available data.

Aspects of the present application address the above-referenced mattersand others.

According to one aspect, a system includes a computed tomography systemincludes a windowing component that receives an ECG signal that includesa premature heart cycle. The ECG signal is time-synchronized with x-rayprojection data of a beating heart. The windowing component positions afirst reconstruction window within a first heart cycle to correspond toa desired cardiac phase when the premature heart cycle causes the firstreconstruction window to correspond to a different cardiac phase. Areconstructor reconstructs projection data corresponding to a pluralityof reconstruction windows from different cardiac cycles to generateimage data indicative of the desired phase of the heart.

According to another aspect, a system includes a windowing componentthat deletes a first reconstruction window that corresponds to asuboptimal cardiac phase due to an anomalous signal in an ECG signal.The ECG signal is mapped in time with x-ray projection data of a beatingheart over a plurality of heart cycles. The windowing component adds areplacement reconstruction window to optimize the reconstruction dataset based on the anomalous signal and available projection data. Areconstructor reconstructs the reconstruction data set to generate imagedata indicative of the desired phase of the heart.

According to another aspect, a system includes a recommendationcomponent that recommends a reconstruction window for a cardiac phasewithin a plurality of successive heart cycles based on an ECG signal andan arrhythmia therein. The ECG signal is obtained while concurrentlyscanning a beating heart with a computed tomography scanner. Areconstructor reconstructs data corresponding to the data for each cyclecorresponding to the reconstruction window.

According to another aspect, a system includes a windowing componentthat automatically repositions or removes a first reconstruction windowfor a heart cycle based on a premature heart cycle within an ECG that issignal synchronized with x-ray projection data of a beating heart. Arecommendation component automatically recommends at least oneadditional reconstruction window based on the premature heart cycle. Areconstructor reconstructs data corresponding to the reconstructionwindows.

According to another aspect, a method includes receiving an ECG signalincluding a premature heart cycle, wherein the ECG signal istime-synchronized with x-ray projection data of a beating heart overmultiple heart cycles, relocating a first reconstruction window within afirst heart cycle that corresponds to data other than a desired cardiacphase due to the premature heart cycle, wherein each of a plurality ofheart cycles includes a reconstruction window; and reconstructing theprojection data corresponding to the plurality of reconstruction windowsto generate image data indicative of the desired phase of the heart.

According to another aspect, a computer readable storage mediumcontaining instructions which, when executed by a computer, cause thecomputer to carry out the method of receiving an ECG signal including apremature heart cycle, relocating a first reconstruction window within afirst heart cycle that corresponds to data other than a desired cardiacphase due to the premature heart cycle, and reconstructing theprojection data corresponding to the plurality of reconstruction windowsto generate image data indicative of the desired phase of the heart.

Still further aspects of the present invention will be appreciated tothose of ordinary skill in the art upon reading and understand thefollowing detailed description.

The invention may take form in various components and arrangements ofcomponents, and in various steps and arrangements of steps. The drawingsare only for purposes of illustrating the preferred embodiments and arenot to be construed as limiting the invention.

FIG. 1 illustrates an exemplary imaging system.

FIG. 2 illustrates a representative ECG signal.

FIG. 3 illustrates a representative ECG signal having an anomalous heartcycle.

FIGS. 4 a, 4 b, 4 c, 4 d, 4 e, 5 a, 5 b, 5 c, 5 d, and 5 e provideexamples in which the system uses the ECG signal having the anomalousheart cycle to select reconstruction data.

FIG. 6 illustrates an example in which a different phase forreconstruction is recommended.

FIG. 7 illustrates an exemplary method.

FIGS. 8, 9, and 10 graphically illustrate an exemplary method.

With reference to FIG. 1, a computed tomography (CT) scanner 100includes a rotating gantry portion 104 which rotates about alongitudinal or z-axis. The portion 104 supports an x-ray source 108such as a x-ray tube, and an x-ray detector 112, which generates x-rayprojection data at a plurality of projection angles or views withrespect to an examination region 116. The detector 112 includes agenerally two-dimensional array of detector elements that generateoutput signals or projection data indicative of the detected radiation.A memory 120 or other storage device stores the projection data.

An object support 124 such as a couch supports a patient or othersubject in the examination region 116. The object support 124 is movableso as to guide the patient or other subject within respect to theexamination region 116 before, during, and after a scan.

A biological monitor 128, such as an electrocardiogram (ECG) or arespiratory monitor, provides information regarding the cardiac phase orother motion state of the subject. The biological monitor 128 signal, inthe case of retrospective gating, is used to correlate the projectiondata with the motion phase or state at which it was acquired.

A processing component 132 communicates with the biological monitor 128and facilitates selecting a set of reconstruction data from theprojection data based on the biological signal. The processing component132 includes an analyzing component 136, a windowing component 140, anda recommendation component 144. These components, individually or acombination thereof, facilitate selecting the set of reconstruction datawhen the biological signal includes an anomalous signal. In oneinstance, the set of data represents the optimal use of the availabledata in the presence of the anomalous signal.

In the case of cardiac CT, one example of such an anomalous signal is anarrhythmia or irregular rhythm such as a premature heart beat orextrasystole. In this case, the analyzing component 136 facilitatesdetermining whether and how a reconstruction window is affected by apremature heart beat. If a reconstruction window is affected by thepremature heart cycle, the windowing component 140 facilitatesadjusting, removing, or adding one or more reconstruction windows basedon the premature heart cycle. The recommendation component 144recommends reconstruction window and cardiac phases based on the on thepremature heart cycle and the available data. These components aredescribed in greater detail below.

A reconstructor 148 reconstructs the selected projection data togenerate image data. In the case of a retrospectively gatedreconstruction, projection data corresponding to one or more desiredmotion states or phases of the subject or a region of interest thereofis reconstructed to generate image data corresponding to the desiredcardiac phase(s).

A general purpose computer serves as an operator console 152. Theconsole 152 includes a human readable output device such as a monitor ordisplay and an input device such as a keyboard and mouse. Softwareresident on the console allows the operator to control and interact withthe scanner 100. In one instance, the interaction includes presentingthe biological signal to an operator, for example, by superimposing areconstruction window identifying a cardiac phase with the biologicalsignal. In addition, the interaction includes allowing the operator tomanually identify an anomaly within the biological signal, generate areconstruction window for a cardiac cycle, select or confirm a set ofdata for reconstruction, invoke automatic data selection andreconstruction, and otherwise interact with the scanner 100, forexample, through a graphical user interface (GUI).

In the examples described below, the system 100 is used for aretrospective gated cardiac CT application. For this application, thebiological monitor 128 provides an ECG signal that is synchronized withprojection data corresponding to multiple heart beats.

FIG. 2 illustrates a representative baseline ECG signal 200 that is“normal” in the sense that it does not include an extrasystole such asarrhythmia or irregular heart beat. Each of the heart cycles 204, 208,212, and 216 includes a systolic period 220 in which the atria (the Pwave) and subsequently the ventricles (the QRS complex) contract and theventricles then re-polarize (the T wave), and a subsequent diastolicperiod 224 in which the heart relaxes after contraction and refills withcirculating blood. The distance 228 between heart cycles or R-Rintervals is represented by time period t. For explanatory purposes, inthis example t is about one (1) second, and each of the systolic anddiastolic periods represents about half of a heart cycle.

Assuming the baseline ECG signal 200 is recorded by the monitor 128,when the ECG signal 200 is received by the console 152, the console 152displays the ECG signal 200 to the operator and provides a mechanism forthe operator to select a desired cardiac phase for reconstruction orotherwise input information indicative of a desired cardiac phase. Inone instance, the input invokes generation of a reconstruction windowfor different portions of the ECG signal 200, each corresponding to thedesired cardiac phase.

By way of example, the operator may provide an input that leads to thegeneration of a reconstruction window for a “quiet” or relativelymotionless cardiac phase of the diastolic period. One such phasegenerally occurs mid to end diastole. In one instance, this phase isapproximated to be at about seventy (70) percent of the time duration ofa heart cycle relative to the peak of the R wave. An exemplaryreconstruction window 236 for this phase is shown in FIG. 2.

Another phase in which the heart is relatively motionless occurs atabout the end of systole. This phase is approximated to be at aboutforty (40) percent of the time duration of the cycle. An exemplaryreconstruction window 232 for this phase is also shown in FIG. 2. Othertechniques for approximating the location of a cardiac phase within theECG signal 200 such as, but not limited to, time based approaches arealso contemplated herein. In addition, the operator may additionally oralternatively select a different cardiac phase.

In general, the width of a reconstruction window is configured so thatthe data acquired over the multiple revolutions provides a complete setof data (or at least one hundred and eighty (180) degrees plus a fanangle of data) for reconstruction. Since the ECG 200 is synchronizedwith the projection data, the reconstruction window identifies theprojection data that corresponds to the desired cardiac phase.

In this example, the system is configured so that the data acquiredduring adjacent heart cycles overlap in the z-axis or longitudinaldirection. The overlapping data acquisitions accommodates heart cycletime duration differences between adjacent heart cycles and mitigatesdata gaps, or instances in which there is a lack of data betweenreconstruction windows corresponding to adjacent heart cycles. Systemparameters such as table pitch are suitably configured based on theindividual's average heart rate, the number and width of the detectorsand the rotation speed in order to provide a suitable table speed forthe overlapping data acquisitions.

FIG. 3 illustrates an ECG signal 300 having a premature heart cycle 312.For this example the heart cycles 304, 308 and 316 are considered“normal” in the sense that they generally occur in time as expected(although they may be affected by the premature heart cycle 312 asdiscussed below) based on the one (1) second time duration intervalsdepicted in the heart cycles in FIG. 2.

The heart cycle 312 is premature in that it occurs earlier thanexpected. In this example, the premature heart cycle 312 occurs sixtenths (0.6) of a second after the R wave of the heart cycle 308 insteadof one (1) second. As a consequence, a diastolic period 320 of thesecond heart cycle 308 is shortened, or ends after six tenths (0.6) of asecond instead of one (1) second after its corresponding R wave.

In addition, a diastolic 324 period of the premature heart cycle 312 isextended. In this example, the diastolic period of the premature heartcycle 312 is prolonged such that the distance from the R wave of theheart cycle 308 to the R wave of the next “normal” heart cycle, theheart cycle 316, is about the same distance as between two normal heartcycles, or about two (2) seconds.

The analyzing component 136, the windowing component 140, and therecommendation component 144 are now further described. In the followingexamples, assume that the ECG signal 300 having the premature heartcycle 312, the identification of the premature cycle 312, and thereconstruction windows and desired cardiac phase are provided to theprocessing component 132.

The analyzing component 136 determines the affect that the prematureheart cycle 312 has on the data identified for reconstruction via thereconstruction window and desired cardiac phase. The heart cycles 304and 316 are not affected by the premature heart cycle 312. As a result,the reconstruction windows within these heart cycles correspond to thedesired cardiac phase.

In contrast, the heart cycles 308 and 312 are affected (as discussedabove) in that the heart cycle 308 is shortened and the heart cycle 312is extended. As a results, a reconstruction window positioned within theheart cycle 308 based on a percentage of the time duration of the heartcycle 308 is located relatively early in time within the heart cycle,and a reconstruction window positioned within the heart cycle 312 basedon a percentage of the time duration of the heart cycle 312 is locatedrelatively later in time within the heart cycle.

With respect to the heart cycle 308, the analyzing component 136determines whether the reconstruction windows occurs prior to or afterthe premature heart cycle 312 in terms of time from the peak of its Rwave.

FIG. 4 a illustrates a case in which a reconstruction window 408 withinthe heart cycle 308 is located, in time relative to a peak of the Rwave, after the premature heart cycle 312. It is to be appreciated thata reference other than the peak of the R wave can alternatively be used.

As depicted, the premature heart cycle 312 occurs at about six tenths(0.6) of a second after the peak of the R wave for the heart cycle 308,and the reconstruction windows 404, 408, 412, and 416 are at aboutseventy (70) percent (%) of their corresponding heart cycle. As aresult, in terms of time after the peak of the R wave the reconstructionwindow 408 is at about forty-two hundredths (0.42) of a second insteadof at about seven tenths (0.7) of a second after the peak of the R wave,as is the reconstruction windows 404 and 416 within the unaffected heartcycles 304 and 316.

The analyzing component 136 recognizes that the reconstruction window408 does not correspond to the desired cardiac phase and that thereconstruction data is suboptimal for reconstruction purposes sinceincludes data corresponding to a different cardiac phase. The windowingcomponent 140 removes the reconstruction window 408 so that thecorresponding data is not selected for reconstruction or reconstructed.This is illustrated in FIG. 4 b. In general, if a reconstruction windowin time after the peak of its corresponding R wave occurs at or laterthan a premature heart cycle, then the reconstruction window is removedso that the corresponding data is not selected for reconstruction orreconstructed.

FIG. 5 a illustrates the case in which a reconstruction window 508within the heart cycle 308 is located, in time relative to the peak ofthe R wave, before the premature heart cycle 312.

As depicted, the premature heart cycle 312 occurs at about six tenths(0.6) of a second after the peak of the relevant R wave, and thereconstruction windows 504, 508, 512, and 516 are at about forty (40)percent (%) of their corresponding heart cycle. In terms of time afterthe peak of the R wave, the reconstruction window 508 is at abouttwenty-four hundredths (0.24) of a second after the peak of itscorresponding R wave instead of at about four tenths (0.4) of a secondafter the peak of the R wave like the reconstruction windows 504 and 516within the unaffected heart cycles 304 and 316.

The heart cycle 308 up to the occurrence of the premature heart cycle312 is regular so the data within this region is normal, or is as if thepremature heart cycle never occurred. The analyzing component 136recognizes that the premature heart cycle 312 has caused thereconstruction window 508 to shift away from the desired cardiac phase,resulting in suboptimal reconstruction data.

The windowing component 140 moves or positions the reconstruction window508 in terms of time so that it is positioned from the peak of its Rwave in terms of time rather than as a percentage of the cycle timeduration. As a result, the reconstruction window is moved to a positionat about four tenths (0.4) seconds from the R wave so that thereconstruction window 508 corresponds to the desired cardiac phase. Thisis illustrated in FIG. 5 b.

With respect to the premature heart cycle 312, the cycle 312 is alwaysabnormal to some degree and therefore optimally it should be removed.The analyzing component 136 determines whether, after removing window412 or 512, a data gap occurs. If there is no data gap, the window 412or 512 is removed as illustrated in FIGS. 4 c and 5 c.

If there is a data gap, then the windowing component 140 makes optimaluse of the data available. For an atrial extrasystole, the cycle 312 isapproximately normal so the reconstruction window 412 is placed at aboutseven tenths (0.7) of a second from the R wave of cycle 312 as shown inFIG. 4 d, and the reconstruction window 512 is placed at aboutfour-tenths (0.28) of a second from the R wave of cycle 312 as shown inFIG. 5 d.

For a ventricular extrasystole, the cycle 312 is more abnormal. Thewindow 412 is placed at about three tenths (0.3) of a second (1second-0.7 seconds) before the next R as shown in FIG. 4 e. The window512 is placed at about four-tenths (0.28) of a second from the R wave ofcycle 312 (like it is for an atrial extrasystole as described above) asshown in FIG. 5 e.

The analyzing component 136 determines whether a data gap occurs if awindow is removed by determining whether the data corresponding to theremaining reconstruction windows would provide sufficient data forreconstruction purposes so that there is no missing data. One techniquefor approximating whether sufficient data exists includes checking tosee whether the inequality in Equation 1 is satisfied:

(T*TS)>(SC*T/RT),

wherein T represents the time interval, TS represents the table speed,SC represents the x-ray beam collimation, and RT represents the x-raysource rotation time. The time interval T is measured from the previousnormal reconstruction window to the reconstruction window of thefollowing normal heart cycle. If the product of the time interval andthe scanner table speed is greater, then a data gap exists and there isnot enough data to reconstruct the image at all z-axis locations.

If repositioning the seventy (70) percent (%) reconstruction windows asdescribed above in connection with FIGS. 4 d and 4 e results in datagaps, then the recommendation component 144 provides a globalrecommendation. For the global recommendation, the recommendationcomponent 144 recommends an entirely new reconstruction at a differentphase(s) located before the premature R wave as shown in FIG. 6. In thisexample, the recommended phase is the forty (40) percent (%) phasedepicted in FIG. 5 a. This ensures a valid reconstruction window for thecycle 308 and provides the option to deciding whether to delete orrelocate the reconstruction window for 312 and, thus, ensures having oneor more reconstruction without data gaps. The seventy (70) percent (%)phase is reconstructed according to FIG. 4 b-e and the new forty (40)percent (%) phase is reconstructed according to FIG. 5 b-e.

FIG. 7 illustrates an exemplary method for selecting optimalreconstruction windows by the system 100. At 704, an ECG signalsynchronized with projection data is obtained. At 708, an anomalousheart cycle such as a premature heart cycle is identified within the ECGsignal, and a desired cardiac phase is selected for reconstruction.Based on this information, the processing component 128 determinesoptimal use of the available data in the presence of the anomaly in theheart signal.

At 712, the analyzing component 132 determines whether the anomalyresults in a reconstruction window that corresponds to a cardiac phaseother than the desired cardiac phase. If not, the reconstruction windowsor the data corresponding to the reconstruction windows is selected forreconstruction.

However, if the anomaly affects the reconstruction data, then at 716 itis determined whether there is sufficient data so that an affectedreconstruction window can be removed without introducing a data gap. Ifthere is sufficient data, then at 720 the reconstruction window isremoved, and the remaining reconstruction windows or the datacorresponding thereto are selected for reconstruction.

Otherwise, at 724, the affected reconstruction window is moved asdescribed above, and the reconstruction windows or the datacorresponding thereto are selected for reconstruction.

At 728, it is determined whether moving the reconstruction windowintroduced a data gap. At 732, if a data has been introduced, then a newreconstruction with sufficient data is also recommended.

FIGS. 8, 9, and 10 graphically show an example. Initially referring toFIG. 8, an exemplary ECG signal with reconstruction windows 804, 808,812, 816, and 820 covering phases located at about seventy-five (75)percent (%) respectively within each heart cycle 824, 828, 832, 836, and840 as illustrated. The heart cycle 836 is identified as an atrialpremature beat (APB).

In this example, the premature heart cycle 836 begins prior to thereconstruction window 812 when the reconstruction window 812 isexpressed in terms of time from a peak of an R wave 848 of the heartcycle 832. Since the reconstruction windows 804-840 are positioned basedon a percentage of the heart cycle and the heart cycle 832 is shortened,the reconstruction window 812 is suboptimal in that is does notcorrespond to the desired cardiac phase at seventy-five (75) percent ofan average heart cycle. As a result, the reconstruction window 812 isremoved, as illustrated in FIG. 9.

Premature heart cycle 836 is abnormal and therefore the system examineswhether window 816 can be removed as well. Since this results in missingdata, an alternative strategy is applied, and the reconstruction window816 is relocated to a more optimal location as shown in FIG. 9 based onthe time from the peak of the R wave of the premature heart cycle 836.

In this example, removing both reconstruction window 812 and 816 resultsin a deficient data for reconstruction purposes, whereas deleting 812and relocating 816 as described above may lead to a suboptimalcorrection. As an alternative solution, a new reconstruction phase of45% corresponding to windows 1002, 1004 and 1008, is recommended asshown in FIG. 10. This now enables window 1006 belonging to prematurecycle 836 to be removed.

Other aspects are now described.

In the illustrated embodiment, the operator identifies the prematureheart cycle within the ECG signal. In an alternative embodiment, theprocessing component 132 automatically identifies anomalous heart cyclesvia a premature heart cycle detector 156. In one instance, theprocessing component 132 prompts the operator for confirmation. Inanother instance, an automatically identified anomalous heart cycle isautomatically considered to be an anomalous heart cycle.

In the illustrated embodiment, the operator provides a desired cardiacphase. In an alternative embodiment, the processing component 132automatically recommends reconstruction windows and/or a reconstructionphase based on the ECG signal and anomalous signal without user inputregarding a desired cardiac phase.

In another embodiment, the processing component 128 automaticallylocates anomalous heart cycles, selects an optimal reconstruction phasebased on an anomalous heart cycle, and generates reconstruction windowsfor each heart cycle. Optionally, the processing component 128automatically invokes reconstruction of the reconstruction data set.

In the above description, the new phase is recommended only when thereis insufficient data. It is to be appreciated that in an alternativeembodiment an additional new phase is always recommended. In oneinstance, this increases the chances of obtaining a good reconstruction.

The processing component 132, including the analyzing component 136, thewindowing component 140, and the recommendation component 144, may beimplemented by way of computer readable instructions which, whenexecuted by a computer processor(s), cause the processor(s) to carry outthe described techniques. In such a case, the instructions are stored ina computer readable storage medium associated with or otherwiseaccessible to the relevant computer.

Note also that the described techniques need not be performedconcurrently with the data acquisition. They may also be performed usinga computer (or computers) which are associated with the scanner 100;they may also be located remotely from the scanner 100 and access therelevant data over a suitable communications network such as a HIS/RISsystem, PACS system, the internet, or the like.

Applications of the forgoing and variations thereof include, but are notlimited to, selecting suitable data for gated CT, magnetic resonanceimaging (MRI), nuclear cardiology and three-dimensional (3D) echostudies.

The invention has been described with reference to the preferredembodiments. Modifications and alterations may occur to others uponreading and understanding the preceding detailed description. It isintended that the invention be constructed as including all suchmodifications and alterations insofar as they come within the scope ofthe appended claims or the equivalents thereof.

1. A system, comprising: a windowing component that receives an ECGsignal that includes a premature heart cycle, wherein the ECG signal istime-synchronized with x-ray projection data of a beating heart, andwherein the windowing component positions a first reconstruction windowwithin a first heart cycle to correspond to a desired cardiac phase whenthe premature heart cycle causes the first reconstruction window tocorrespond to a different cardiac phase; and a reconstructor thatreconstructs projection data corresponding to a plurality ofreconstruction windows from different cardiac cycles to generate imagedata indicative of the desired phase of the heart.
 2. The system ofclaim 1, wherein the windowing component repositions the firstreconstruction window in terms of time relative to a reference signalwithin the first heart cycle when a first time interval from thereference signal to the first reconstruction window is less than asecond time interval from the reference signal to the premature heartcycle.
 3. The system of claim 1, wherein the windowing component removesthe first reconstruction window when a first time interval from thereference signal to the first reconstruction window is greater than asecond time interval from the reference signal to the premature heartcycle.
 4. The system of claim 3, further including a recommendationcomponent, wherein the recommendation component recommends a differentphase that ensures that the first time interval from the referencesignal to the first reconstruction window is less than the second timeinterval from the reference signal to the premature heart cycle.
 5. Thesystem of claim 1, wherein the first heart cycle is the premature heartcycle.
 6. The system of claim 5, wherein the windowing componentattempts to remove the first reconstruction window on condition that nodata gap occurs.
 7. The system of claim 5, wherein the windowingcomponent repositions the first reconstruction window in terms of timerelative to a reference signal within the first heart cycle when thepremature heart cycle is an atrial extrasystole.
 8. The system of claim5, wherein the windowing component repositions the first reconstructionwindow in terms of time relative to a reference signal in a subsequentheart cycle when the premature heart cycle is a ventricularextrasystole.
 9. The system of claim 1, further including arecommendation component, wherein the recommendation componentrecommends a second phase for reconstruction when the second phase has arelatively higher probability of having sufficient data forreconstruction after removing a reconstruction window due to thepremature heart cycle.
 10. The system of claim 8, further including aconsole, wherein an operator provides an input via the console thatconfirms or rejects the recommended cardiac phase for reconstruction.11. The system of claim 1, further including a console, wherein anoperator provides an input via the console that identifies the prematureheart cycle within the ECG signal.
 12. (canceled)
 13. A system,comprising: a windowing component that deletes a first reconstructionwindow that corresponds to a suboptimal cardiac phase due to ananomalous signal in an ECG signal, wherein the ECG signal is mapped intime with x-ray projection data of a beating heart over a plurality ofheart cycles, and wherein the windowing component adds a replacementreconstruction window to optimize the reconstruction data set based onthe anomalous signal and available projection data; and a reconstructorthat reconstructs the reconstruction data set to generate image dataindicative of the desired phase of the heart.
 14. The system of claim13, wherein the anomalous signal is a premature heart beat.
 15. Thesystem of claim 13, further including a recommendation component thatrecommends the replacement reconstruction window
 16. The system of claim13, wherein the windowing component automatically adds the replacementreconstruction window.
 17. The system of claim 13, further including ananomalous signal finder that automatically locates and identifies theanomalous signal in the ECG signal.
 18. The system of claim 13, whereinthe windowing component moves at least a second reconstruction windowwithin a heart cycle to correspond to the desired cardiac phase when theanomalous signal causes the second reconstruction window to correspondto a different cardiac phase.
 19. The system of claim 13, wherein thewindowing component adds a second reconstruction window if a firstproduct of a time interval from a previous normal reconstruction windowto a subsequent normal reconstruction window and a speed of a support ina longitudinal direction is greater than a second product of acollimation of an x-ray beam and an x-ray source rotation time dividedby the time interval.
 20. A system, comprising: a recommendationcomponent that recommends a reconstruction window for a cardiac phasewithin a plurality of successive heart cycles based on an ECG signal andan arrhythmia therein, wherein the ECG signal is obtained whileconcurrently scanning a beating heart with a computed tomographyscanner; and a reconstructor that reconstructs data corresponding to thedata for each cycle corresponding to the reconstruction window.
 21. Thesystem of claim 20, wherein the reconstruction window corresponds to agenerally motionless state of the heart.
 22. The system of claim 20,wherein the reconstruction window corresponds to data having arelatively high probability of having no data gaps after removing areconstruction window due to the arrhythmia.
 23. The system of claim 20,wherein an operator selects an initial cardiac phase and the recommendedreconstruction window corresponds to a different cardiac phase.
 24. Thesystem of claim 20, wherein the recommendation component recommends atleast a second reconstruction window that corresponds to a differentcardiac phase.
 25. A system, comprising: a windowing component thatautomatically repositions or removes a first reconstruction window for aheart cycle based on a premature heart cycle within an ECG that issignal synchronized with x-ray projection data of a beating heart; arecommendation component that automatically recommends at least oneadditional reconstruction window based on the premature heart cycle; anda reconstructor that reconstructs data corresponding to thereconstruction windows.
 26. The system of claim 25, wherein thereconstruction data represents an optimal set of data in that itincludes a complete set of data for reconstruction and reduces artifactintroduced from reconstructing data corresponding to different cardiacphases.
 27. (canceled)
 28. A method, comprising: receiving an ECG signalincluding a premature heart cycle, wherein the ECG signal istime-synchronized with x-ray projection data of a beating heart overmultiple heart cycles; relocating a first reconstruction window within afirst heart cycle that corresponds to data other than a desired cardiacphase due to the premature heart cycle, wherein each of a plurality ofheart cycles includes a reconstruction window; and reconstructing theprojection data corresponding to the plurality of reconstruction windowsto generate image data indicative of the desired phase of the heart. 29.The method of claim 28, further including relocating a secondreconstruction window within the premature heart cycle relative to areference signal in the premature heart cycle in terms of time orrelative to a reference signal in a next heart cycle in terms of time,depending on type of premature heart cycle.
 30. The method of claim 28,further including removing the first reconstruction window.
 31. Themethod of claim 28, further including recommending reconstructing datafor a second different cardiac phase.
 32. The method of claim 28,further including adding at least one reconstruction window thatcorresponds to a different cardiac phase.
 33. (canceled)
 34. (canceled)